The present invention relates to a bending device for an endoscope which provides a bending operation for a bendable portion of the endoscope by moving back and forth an operating wire.
In general, medical endoscopes for observing and treating a coelom such as the stomach and intestines and industrial endoscopes for observing the inside of a tube such as used in a boiler and a chemical plant require to have a bendable function to direct the distal end of the insertable portion thereof to a desired direction.
To this end, such endoscope is provided with a bending device in which a guide sheath for operating wires comprising a pair of coil sheaths which are flexible but do not lengthen or shorten in the axial direction is inserted into the insertable portion of the endoscope and operating wires are respectively inserted into the pair of coil sheaths so as to provide the bending operation to the bendable portion of the endoscope by moving back and forth the operating wires. Specifically, the coil sheath, which generally employs a closely wound coil, has a structure in which one end of the operating wire inserted in the closely wound coil is fixed to the distal end of the bendable portion and the other end thereof is connected to a bending operation portion which is provided in the operation portion of the endoscope so that the bending operation can be performed by moving back and forth the operating wires at the bending operation portion. With this structure, however, looseness would be caused between the coil sheath and the operating wire during the bending operation, which is caused by shrinkage of a bendable tube of the bendable portion and the coil sheath and elongation of the operating wire and the like.
In the case where the bending operation is performed by pulling the strained operating wire as described above, a compressive force is applied to a closely wound coil which forms the coil sheath.
The compressive force is twisted in a direction in which the closely wound coil is running down to act so as to axially shorten its length. Accordingly, when the bending operation is repeated, the closely coiled winding is reduced in length in its axial direction to cause looseness in the operating wire.
Such looseness involves a play which causes a phenomenon in which no bending is operated until the looseness is canceled, even when an operating lever or the like is moved, and reduction in a bending angle by a value initially being loosened to lower the insertability and the performance of observation and treatment of the endoscope.
A technique of canceling looseness is proposed, for example, in Japanese Utility Model Publication Sho59-31202.
In the proposed technique, a screw member is interposed in a part of an operating wire so as to change threadably engaging position of the screw member, thereby a distance between connecting portions of the screw member being changed by the screwing operation to adjust a length of the operating wire to cancel looseness.
In such technique, however, repairs and adjustments should be made whenever looseness is caused. Such corrrecting operation has to be conducted by a specialist, so that it interrupts the use of an endoscope and also is very expensive.